It is well documented that the elderly and post-surgical patients are at a heightened risk of falling. These individuals are often afflicted by gait and balance disorders, weakness, dizziness, confusion, visual impairment, and postural hypotension (i.e., a sudden drop in blood pressure that causes dizziness and fainting), all of which are recognized as potential contributors to a fall. Additionally, cognitive and functional impairment, and sedating and psychoactive medications are also well recognized risk factors.
A fall places the patient at risk of various injuries including sprains, fractures, and broken bones—injuries which in some cases can be severe enough to eventually lead to a fatality. Of course, those most susceptible to falls are often those in the poorest general health and least likely to recover quickly from their injuries. In addition to the obvious physiological consequences of fall-related injuries, there are also a variety of adverse economic and legal consequences that include the actual cost of treating the victim and, in some cases, caretaker liability issues.
In the past, it has been commonplace to treat patients that are prone to falling by limiting their mobility through the use of restraints, the underlying theory being that if the patient is not free to move about, he or she will not be as likely to fall. However, research has shown that restraint-based patient treatment strategies are often more harmful than beneficial and should generally be avoided—the emphasis today being on the promotion of mobility rather than immobility. Among the more successful mobility-based strategies for fall prevention include interventions to improve patient strength and functional status, reduction of environmental hazards, and staff identification and monitoring of high-risk hospital patients and nursing home residents.
Of course, direct monitoring of high-risk patients, as effective as that care strategy might appear to be in theory, suffers from the obvious practical disadvantage of requiring additional staff if the monitoring is to be in the form of direct observation. Thus, the trend in patient monitoring has been toward the use of electrical devices to signal changes in a patient's circumstance to a caregiver who might be located either nearby or remotely at a central monitoring facility, such as a nurse's station. The obvious advantage of an electronic monitoring arrangement is that it frees the caregiver to pursue other tasks away from the patient. Additionally, when the monitoring is done at a central facility a single person can monitor multiple patients which can result in decreased staffing requirements.
Generally speaking, electronic monitors work by first sensing an initial status of a patient, and then generating a signal when that status changes, e.g., he or she has sat up in bed, left the bed, risen from a chair, etc., any of which situations could pose a potential cause for concern in the case of an at-risk patient. Electronic bed and chair monitors typically use a pressure sensitive switch in combination with a separate electronic monitor which conventionally contains a microprocessor of some sort. In a common arrangement, a patient's weight resting on a pressure sensitive mat (i.e., a “sensing” mat) completes an electrical circuit, thereby signaling the presence of the patient to the microprocessor. When the weight is removed from the pressure sensitive switch, the electrical circuit is interrupted, which fact is similarly sensed by the microprocessor. The software logic that drives the monitor is typically programmed to respond to the now-opened circuit by triggering some sort of alarm—either electronically (e.g., to the nursing station via a conventional nurse call system) or audibly (via a built-in siren) or both. Additionally, many variations of this arrangement are possible and electronic monitoring devices that track changes in other patient variables (e.g., wetness/enuresis, patient activity, etc.) are available for some applications.
General information relating to mats for use in patient monitoring may be found in U.S. Pat. Nos. 4,179,692, 4,295,133, 4,700,180, 5,600,108, 5,633,627, 5,640,145, and 5,654,694 (concerning electronic monitors generally). Additional information may be found in U.S. Pat. Nos. 4,484,043, 4,565,910, 5,554,835, and 5,623,760 (switch patents), the disclosures of all of which are all incorporated herein by reference.
By way of general background, in a typical arrangement, a pressure-sensing mat of the sort discussed herein is a sealed “sandwich” composed of three layers: two outer layers and an inner (central) layer positioned between the two outer layers. The outer layers are usually made of some sort of plastic and are impermeable to fluids and electrically non-conductive on their outer faces, where “outer” is determined with respect to the middle layer. The inner surface of each of the outer layers—which inner surfaces are oriented to face each other from opposite sides of the central layer—is made to be electrically conductive, usually by printing a conductive (e.g., carbon-based) ink on that surface. The compressible middle “central spacer” is made of a non-conductive material and serves to help keep the two conductive faces apart when a patient is not present on the sensor. The central spacer is discontinuous, which makes it possible for the two conductive inner surfaces to be forced into contact through the one or more discontinuities when weight is applied to the switch. By attaching a separate electrical lead to each of the conductive inner faces, it can readily be determined via a simple continuity (or low voltage) check whether a weight is present on the sensor (e.g., a patient is seated thereon). Removal of the weight causes the central spacer to expand and press apart the two conducting faces, thereby breaking the electrical connection between them. Thus, a device that monitors the resistance across the two electrical leads may determine when a patient has moved from a seated or prone position.
One disadvantage of the current generation of pressure sensitive mats is that they cannot be completely (e.g., hermetically) sealed around their perimeters against the external environment. The reason for this should be clear: if the interior of the mat were completely sealed, air pressure inside of the mat would tend to oppose the urging of the mat faces into contact, thereby making it difficult or impossible to complete the circuit (e.g., think of compressing an “air pillow”). Of course, the fact that the interior of the mat must be kept open to the atmosphere results in a mat that is highly susceptible to invasion by bodily fluids or cleaning solutions, as the in-rushing air that enters when the switch expands tends to carry fluids along with it into the interior of the mat. Further, it is well known that some common disinfecting cleaners can loosen the adhesives that hold the layers of a conventional mat together, thereby ruining the sensor. Thus, cleaning soiled mats becomes problematic. In summary, what is needed is a pressure sensitive mat that is more resistant to invasion by fluids than has heretofore been available.
Methods of manufacturing conventional pressure sensitive mats for use in medical applications of this sort of sensing device typically begin at a single station punch, wherein the upper and lower plastic/nonconductive members are cut from a larger sheet of material. This step would typically be followed by the application of a conductive material to one face of each member. For example, the conductive material could be printed onto the surface using a carbon-based ink, although other variations have been employed. A popular alternative method involves the use sheets or rolls of material on which the conductor has been pre-applied.
The inner non-conductive member may be a discrete layer of material that has dimensions somewhat smaller than those of the exterior member, or it could take the form of a pattern of non-conductive raised ridges or dots which is deposited on top of the ink (the raised ridges separating the two conductive faces wherever they are present). Either way, the non-conductive material must be discontinuous to the extent that it allows the conductive materials to come into contact when the assembled mat is compressed. Thereafter, separate isolated electrical leads are attached to the inner faces of the mats so that they make contact with the conductive surface. The two conductive inner surfaces are oriented so that they face each other across the insulating layer and, if a separate central spacer is used, it is positioned between them. Finally, the apparatus is sealed at its edges to protect against invasion of moisture, typically through the use of an adhesive that is applied to the edges of the facing members.
However, mats assembled in this manner are subject to a variety of well-known problems. For example, if the non-conductive member is bent, it is possible to introduce breaks in the conductive ink pattern that has been printed thereon. If the break extends the width of the conductive surface, dead (i.e., nonresponsive) regions may be created in the mat or the mat may cease to function altogether.
Additionally, the seal between the two outer members is dependent on the quality of the adhesive bond between them. Depending on the choice of adhesive and the environmental conditions at the time the seal was formed—e.g., the relative humidity, temperature, etc.—the adhesion between the two outer members may be imperfect, which can allow moisture into the interior of the assembled device, thereby shortening its active and or shelf life.
Further, prior art mats are susceptible to cord pull out and may fail to open after being compressed, which failure is often because the air inside has been expelled and air pressure continues to hold the halves of the mat together after weight is removed.
Because of variability that is inherent in the current technology of printing conductive inks—which is typically done via some sort of screening process—the mats produced thereby can be unreliable and it can be difficult to create printed mats that exhibit specific electrical properties when the circuit is closed. Further, the screen process does not lend itself to repeatability, so it can be difficult, say, to produce a mat that has a particular resistance when closed.
Finally, and more generally, those of ordinary skill in the art will recognize that electronic equipment is subject to infiltration and attack by foreign gases, solids and liquids. Of course, the presence of such foreign compounds can damage or destroy sensitive electronic components. Externally operated switches are especially prone to contamination because they are usually located on the exterior of the device where they can be accessed by the user. As a consequence, membrane switches have become a staple in many settings because of their impermeability to most gases and chemicals and the ease with which they can be manufactured and marked.
However, conventional methods of manufacture of membrane switches require the creation of a mold or a hardened polished die which adds substantially to the cost of manufacture. Further, currently known methods of manufacture utilize a hydraulic or similar high pressure press to form the switches from the raw materials. Thus, what is needed is a method of manufacturing membrane switches which can be implemented using equipment made of softer metals (e.g., aluminum) which are cheaper to form. Of course, softer metals are only feasible if the pressure required to form the switches can be reduced, e.g. to presses utilizing pneumatic (rather than hydraulic) energy.
Heretofore, as is well known in the patient monitoring and switch arts, there has been a need for an invention to address and solve the above-described problems. Accordingly, it should now be recognized, as was recognized by the present inventor, that there exists, and has existed for some time, a very real need for a electronic patient monitor that would address and solve the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.